Field of the Invention
The present invention relates to a method and an apparatus for controlling a gas turbine combustor.
Description of Related Art
In the gas turbine combustor, there are a diffusion combustor and a premix combustor available. The diffusion combustor is a system for separately feeding and burning fuel and air in a combustion chamber, and a flame is formed in a state close to the stoichiometric ratio of fuel to air, and the local flame temperature rises, so that although the combustion stability is high, the nitrogen oxide (NOx) emission increases.
On the other hand, the premix combustor is a system for premixing fuel and air and then feeding and burning them in the combustion chamber, and the mixing ratio of fuel and air on the flame sheet is lower than that in the diffusion combustion, and the local flame temperature is lowered, so that the emission of NOx can be reduced.
As general use of a low NOx combustor, at the time of a low load operation from start up to acceleration, the diffusion combustion of high combustion stability is used and at the time of the base load operation from a partial load, the diffusion combustion of high combustion stability and the premix combustion capable of reducing the NOx emission are combined, thus the combustion stability and the reduction in the NOx discharging rate are compatible with each other.
When using the gas turbine for power generation, the gas turbine needs to withstand a load dump when the load operation state is transferred to the no-load operation state due to separation of the generator from the gas turbine. The load dump is to urgently separate the generator and turbine from each other from some cause and in this case, the gas turbine needs to immediately enter the full speed no-load operation state.
Immediately after the load dump, the rotating speed of the gas turbine increases. If the rotating speed of the gas turbine increases to the limit value or higher, there is a concern that it may lead to damage to the compressor or turbine and it is necessary to promptly reduce the fuel flow rate to the minimum limit capable of maintaining the flame by the gas turbine combustor, thereby suppressing an increase in the rotating speed of the gas turbine.
Due to the increase in the rotating speed of the gas turbine in correspondence to the load dump, the flow rate of compressed air flowing into the gas turbine combustor increases, and the fuel flow rate reduces suddenly, so that the inner state of the gas turbine combustor is transiently greatly changed. Therefore, in the gas turbine combustor, high combustion stability is required, and when reducing the fuel flow rate at the time of load dump, so as to dump the fuel for premix combustion, thereby switch to the independent diffusion combustion, the fuel flow rate is controlled.
In Japanese Patent Laid-open No. Hei 10 (1998)-169467 of a prior art, at the time of load dump of the gas turbine, an art capable of switching the premix combustion to the independent diffusion combustion without delay of ignition is disclosed.
Patent Document 1: Japanese Patent Laid-open No. Hei 10 (1998)-169467